The invention is based on a piston pump that is intended for use in a hydraulic brake system of a vehicle.
Such piston pumps are known per se; as an example, reference may be made to the piston pump disclosed in German Patent Application DE 41 07 979 A1. The known piston pump has a pump housing with a pump bore disposed in it, in which bore a bush is inserted. A piston, which can be driven into an axially reciprocating stroke motion is axially displaceably received in the bush. It is also known for the piston to be inserted axially displaceably into the pump housing directly, without a bush.
A problem in the known piston pumps is their aspiration performance, especially at low temperatures and with fluid to be pumped that is consequently viscous. Narrow line cross sections, bent line courses, and throttle restrictions at screw fastenings or hydraulic components such as the master cylinder, magnet valves and check valves, create high flow resistance on an intake side of the piston pump and thereby retard a pressure buildup by means of the piston pump.
For this reason, in German Patent Application DE 41 28 368 A1, whose subject is a vehicle hydraulic brake system with a traction control device using a piston pump, it is proposed that a pressure fluid reservoir be provided on the intake side of the piston pump, the reservoir making an additional fluid volume available to the piston pump in order to smooth out pressure pulsations. However, the known vehicle brake system has the disadvantage that the pressure fluid reservoir entails an increased production cost. A further factor is that an additional fluid volume represents additional elasticity, which makes the vehicle brake system actuation softer or "spongier", leading to an inaccurate pressure point upon actuation of the vehicle brake system.